Plastic substrates used in various applications are generally weak to ultraviolet light, when being exposed continuously with sun light, they suffer from breakage of polymer main chain gradually, resulting in a gradual lowering of strength as a substrate. Thus, a lot of studies have been done on providing an absorbing layer of ultraviolet light for these plastic substrates (for example, Japanese Unexamined Patent Publication No. H11-40833, Japanese Unexamined Patent Publication No. 2003-107690 and Japanese Unexamined Patent Publication No. 2004-126345).
In particular, polyester type films typified by polyethylene terephthalate (PET) are excellent in dimensional stability, heat resistance, transparency, strength and the like, so that they are also used widely in optical applications, but, polyester for film ordinarily employs aromatic  dicarboxylic acid as a raw material, and therefore, it contains an aromatic ring in the backbone of polyester. The aromatic ring is deteriorated and colored by ultraviolet light to generate yellowing of the film, so that an ultraviolet absorbing layer is required more than other plastics.
However, polyesters like PET crystallize easily, particularly, stretched films are poor in adhesion due to high crystalline orientation and have a weak adhesion to a layer to be laminated. Thus, ordinarily, polyester type films are subjected to adhesion enhancing treatments such as corona discharge treatment, plasma treatment, treatment using an alkali metal compound solution, high frequency sputter etching treatment and formation of easy adhesion layer (undercoat layer) to laminate an ultraviolet absorbing layer (e.g. Japanese Unexamined Patent Publication No. H11-348199). For example, while an untreated PET film has a surface wetting index of about 35 mN/m measured according to JIS K-6768 in 2004 version, when the adhesion enhancing treatment is conducted, the index can be increased to 50 mN/m or more; as a result, the adhesion to ultraviolet absorbing layers is remarkably improved.
However, there are many treatments with difficult condition arrangements in the above adhesion enhancing treatments, and there needs also an additional step, so that it is required to skip the adhesion enhancing treatment from the point of saving costs as well.
Also, in the inventions of Japanese Unexamined Patent Publication No. H11-40833, Japanese Unexamined Patent Publication No. 2003-107906 and Japanese Unexamined Patent Publication No. 2004-126345 described above, adhesion to untreated PET films is not sufficient, and some cases  were poor in stability of resin liquids for forming ultraviolet absorbing layers. Further, crosslinkers requiring longer time and higher temperature to crosslink are used in some cases, so there existed a room for improvement from the point of saving costs.
Meanwhile in the fields of thin model display and mobile phone, in addition to cost cutting by shortening steps, further miniaturization of each of members i.e. thinner type and weight saving are required. Out of these members, there is a thin film having ultraviolet absorbing performance, and in the case of one side lamination on a substrate with an ultraviolet absorbing layer, upon hardening the ultraviolet absorbing layer, its volume shrinks to cause the film to curl remarkably in some cases. When such curl occurs, there have been problems that troubles take place upon lamination in the following step with other functional layers such as a hard coat layer and an adhesive layer, and films are abraded due to contact with rolls, and therefore, particularly, productivity of film in an optical application is remarkably lowered.